The Labour leader said he had no symptoms and will be working from home until Monday 1 February in line with government advice.
It is the third time Sir Keir has been forced to self-isolate after a member of his team tested positive for Covid-19 in December and a relative showed symptoms of the virus in September.
It was not immediately clear whether he will face Boris Johnson virtually at prime minister’s questions on Wednesday or delegate the responsibility to deputy leader, Angela Rayner.
Under the government’s instructions, individuals who are told to self-isolate by the Test and Trace service or the NHS Covid-19 app must not leave the home for any reason.
A period of self-isolation lasts for 10 days from the first point of contact with a Covid-positive person, meaning the initial contact came late last week.
Writing on Twitter, Sir Keir said: “This morning I was notified that I must self-isolate after coming into contact with someone who has test positive for Covid-19. I have no symptoms and will be working from home until next Monday.”
